The Spatial Extension of the Field Scattered by Silver Nanoparticles Excited near Resonance as Observed by Apertureless Near-Field Optical Microscopy

We report an investigation of the field scattered by isolated silver nanoparticles on a glass substrate observed by apertureless near-field optical microscopy with an illumination wavelength of 404 nm. We observe an unexpected spatial extension of the scattered field. The near-field contrast (both distribution and intensity) is shown to be strongly sensitive to polarization of the incident light. A large (×10) field enhancement observed in transverse magnetic (TM) polarization is interpreted to be the result of the contribution of the particle plasmon resonance to the diffracted field. The results are further discussed in terms of the particle shape and the experimental configuration used. [DOI: 10.1143/JJAP.41.L351]